[FIR] KT-57220 Avoid creating useless synthetic function providers

- This optimization applied to LL FIR can be extended to K2 as a whole.
  Likely, there won't be any performance benefits in CLI runs, but it's
  still better to avoid useless symbol providers.

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/sessions/LLFirSessionCache.kt

@@ -164,13 +164,8 @@ internal class LLFirSessionCache(private val project: Project) {
             })
 
             val javaSymbolProvider = createJavaSymbolProvider(this, moduleData, project, contentScope)
-
-            // We only need to add an extension synthetic function provider if the session's function type service even has extension kinds.
-            // Otherwise, the provider will be completely useless.
-            val syntheticFunctionalInterfaceProvider = if (this.functionTypeService.hasExtensionKinds()) {
-                FirExtensionSyntheticFunctionInterfaceProvider(this, moduleData, scopeProvider)
-            } else null
-
+            val syntheticFunctionInterfaceProvider =
+                FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(this, moduleData, scopeProvider)
             register(
                 FirSymbolProvider::class,
                 LLFirModuleWithDependenciesSymbolProvider(
@@ -179,7 +174,7 @@ internal class LLFirSessionCache(private val project: Project) {
                         provider.symbolProvider,
                         switchableExtensionDeclarationsSymbolProvider,
                         javaSymbolProvider,
-                        syntheticFunctionalInterfaceProvider,
+                        syntheticFunctionInterfaceProvider,
                     ),
                     dependencyProvider,
                 )